Print media feed alignment mechanism

ABSTRACT

To maintain quality printed images in high speed photographic quality printing it is necessary to ensure accurate registry of the print media with the printheads. To ensure this result an alignment mechanism is provided for the stack of print media to be fed to the printer. The alignment mechanism comprises a receptacle to hold the stack of print media, a registry stop and a tapping mechanism located opposite the registry stop, to maintain the stack of print media in accurate abutment with the registry stop.

[0001] Divisional Application of U.S. Ser. No. 10/052,425 filed on Jan.23, 2002

FIELD OF THE INVENTION

[0002] This invention relates to a high speed, photographic qualityprinter. More particularly, the invention relates to a method ofseparating a sheet of print media from a stack of sheets, the sheetsbeing porous.

BACKGROUND TO THE INVENTION

[0003] The applicant has developed various printheads which provide highspeed, photographic quality printing. The printheads comprise ink jetnozzles arranged in an array. The ink jet nozzles are formed usingmicroelectromechanical systems (MEMS) technology. The use of MEMStechnology results in very high speed printing capabilities where pagescan be printed at a rate of up to two pages per second (for double-sidedprinting).

[0004] To facilitate such high speed printing, it is important, firstly,that the paper fed to the printing station of the printer is accuratelyaligned and capable of the required feed rate with as little likelihoodas possible of paper jams or the like, occurring. Secondly, the papermust be able to be fed to the printing station at a rate sufficient touse the high speed printing capabilities of the printing station to itsfullest extent.

SUMMARY OF THE INVENTION

[0005] According to the invention, there is provided a method ofseparating a sheet of print media from a stack of sheets, the sheetsbeing porous and the method including the steps of:

[0006] blowing fluid on to a top surface of a topmost sheet of the printmedia on the stack so that the fluid passes through at least the topmostsheet of the stack; and

[0007] capturing at least a part of the topmost sheet for conveyance toa printing station of a printer.

[0008] The method may include blowing the fluid on to the top surface ofthe topmost sheet through an aperture means of a pick up means of aprint media feed arrangement. The pick up means may be in the form of apick up bar. The aperture means of the pick up bar may be in any of anumber of different forms. For example, the aperture means may be in theform of a channel extending longitudinally along the bar. Instead, thebar may support a plurality of longitudinally spaced, discrete orifices,the orifices defining the aperture means.

[0009] The method may include, initially, prior to capturing said atleast part of the topmost sheet, lifting said at least part of thetopmost sheet from the stack. The method may include causing saidlifting of said at least a part of the topmost sheet by creating a lowpressure region between a face of the pick up means and the top surfaceof the topmost sheet of print media.

[0010] Preferably, the method includes maintaining the pick up means inspaced relationship relative to the top surface of the topmost sheet ofprint media to cause said low pressure region.

[0011] The method may include capturing said at least part of thetopmost sheet of print media by the pick up means, preferably byreversing a direction of fluid flow through the pick up means to cause achange from a blowing action to a suction action.

[0012] The method may include conveying said topmost sheet of printmedia in a direction substantially normal to a direction of flow offluid blown on to the stack.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is now described by way of example with referenceto the accompanying drawings in which:

[0014]FIG. 1 shows a part of a printer including a print media feedarrangement operated in accordance with the method of the invention;

[0015]FIG. 2 shows a three-dimensional view of an input region of theprinter including part of the print media feed arrangement;

[0016]FIG. 3 shows a three dimensional view, on an enlarged scale, ofthe part of the print media feed arrangement of FIG. 2;

[0017]FIG. 4 shows a schematic, sectional side view of an initial stageof operation of the print media feed arrangement;

[0018]FIG. 5 shows a schematic, sectional side view of a second stage ofoperation of the print media feed arrangement;

[0019]FIG. 6 shows a schematic, sectional side view of a third stage ofoperation of the print media feed arrangement; and

[0020]FIG. 7 shows a schematic, sectional side view of a fourth stage ofoperation of the print media feed arrangement.

DETAILED DESCRIPTION OF THE DRAWINGS

[0021] Referring initially to FIG. 1 of the drawings, a part of aprinter is illustrated and is designated generally by the referencenumeral 10. The printer 10 is a high speed printer which prints bothsides of print media at the rate of approximately one sheet per secondor two pages per second (i.e. both sides of the sheet). The print mediais, in this case, in the form of a stack of sheets. For ease ofexplanation, the invention will be described with reference to the printmedia being a stack of A4 sheets of paper and, more particularly, sheetsof paper having a predetermined degree of porosity.

[0022] The printer 10 uses a pair of opposed page width printheads 12,arranged at a printing station 13, to print on both sides of sheets ofpaper fed through the printing station 13. Each printhead 12 is in theform of a microelectromechanical systems (MEMS) chip having an array ofink jet nozzles to achieve the high speed, photographic quality printingdesired.

[0023] The printing station 13 includes a set of primary rollers 14,comprising a drive roller 16 and a driven roller 18, arranged upstreamof the printheads 12 to convey a sheet of paper to the printheads 12. Asecondary set of rollers 20, comprising a first roller 22 and a secondroller 24, is arranged intermediate the printheads 12 and the set ofprimary rollers 14. A paper deflector 26 is arranged between the sets ofrollers 14 and 20.

[0024] As illustrated more clearly in FIG. 2 of the drawings, the printmedia is, as described above, arranged in a stack 28. The stack 28 isreceived in a bin (not shown) of the printer 10 and is retained againsta metal bulkhead 30 of the printer 10 in a suitable cabinet (also notshown). A tapping mechanism 32, which is solenoid driven, taps the paperstack 28 to ensure that the sheets of the paper stack 28 are maintainedin accurate abutment with the metal bulkhead 30 so that, when a sheet isfed is to the printing station 13, as will be described in greaterdetail below, the sheet lifted from the stack 28 is aligned to be inregister with the printheads 12. In other words, the tapping mechanism32 inhibits skewing of a sheet picked from the stack 28.

[0025] The printer 10 includes a paper feed arrangement 34 for feeding asheet of paper from the stack 28 to the rollers 16 and 18 of the set ofprimary rollers 14 so that the sheet of paper can be transported to theprinting station 13 for printing.

[0026] The feed arrangement 34 comprises a pivot rod or axle 36 which isrotatably driven by a drive means in the form of a stepper motor 38. Aswing arm 40 is arranged at each end of the axle 36.

[0027] The paper feed arrangement 34 includes a pick up bar 42 which isconnected to a fluid hose 44. The pick up bar 42 is pivotally attachedto the swing arms 40. An arm 46, having a bifurcated end (not shown)projects from one end of the bar 42. The arm 46 is slidably received ina sleeve in the form of a pivot block 48. The arm 46 and, moreparticularly, its bifurcated end, cooperates with an optical sensor 50to determine when the pick up bar 42 is in its home position, the homeposition of the pick up bar 42 being shown, schematically, in FIG. 4 ofthe drawings.

[0028] As described above, the printer 10 is a high-speed printer whichhas a capacity to print at the rate of one sheet per second. To make useof this capability, it is important that the sheets of paper are fedindividually to the printing station 13 from the stack 28 in anaccurate, controlled manner. Consequently, it is necessary for the pickup bar assembly 34 to separate a sheet to be transported to the printingstation 13 from the stack 28 accurately. To separate a topmost sheet28.1 from the stack 28, the fluid hose 44 is connected to a fluid source(not shown). Air is blown down the hose 44 in the direction of arrow 52as shown in FIG. 4 of the drawings. The air exits through an outletaperture 54 of the pick up bar 42 as shown by the arrows 56. The air isforced between a foot portion 58 of the pick up bar 42 and the topmostsheet 28.1 of the paper stack 28.

[0029] The invention is intended particularly for use with print mediawhich is porous such as, for example, 80 gsm paper.

[0030] Due to the porosity of the paper, air is also driven through thetopmost sheet 28.1 and impinges on a sheet of the stack 28 which issecond from the top, as shown by arrow 60 in FIG. 5 of the drawings.This results in an initial separation of the topmost sheet 28.1 from theremainder of the sheets of the stack 28.

[0031] Also, as a result of localised low pressure occurring between aperiphery of the foot portion 58 of the pick up bar 42 and the topmostsheet 28.1 of the stack 28, the topmost sheet 28.1 is attracted to thepick up bar 42 as shown in FIG. 6 of the drawings. Due to the passage ofair through the topmost sheet 28.1 separation of the topmost sheet 28.1from the remainder of the sheets of the paper stack 28 is aided.

[0032] Once the sheet 28.1 has been lifted off the stack 28 andtransported a short distance from the stack 28 and when the pick up bar42 reaches a predetermined altitude relative to the stack 28, thedirection of flow of the air is reversed so that a suction effect isimparted at the aperture 54 of the pick up bar 42. This is shown in FIG.7 of the drawings by arrows 62.

[0033] As the swing arms 40 of the paper feed arrangement 34 continue torotate in the direction of arrow 64 (FIG. 3 of the drawings), the pickup arm 42 moves in the direction of arrow 66 (FIG. 7) so that a leadingedge of the topmost sheet 28.1 of the paper stack 28 is fed between therollers 16 and 18 of the set of primary drive rollers 14. The suction isthen shut off in the hose 44 so that the sheet 28.1 is released from thepick up bar 42 for onward conveyance by the sets of rollers 14 and 20 tothe printing station 13 for printing purposes.

[0034] It will be appreciated that the airflow parallel to a surface ofthe topmost sheet 28.1 of the stack 28 results in a low friction cushionwhich facilitates translational motion of the sheet 28.1 relative to thepick up bar 42. This allows the sheet 28.1 to be moved by any suitablemethod in a direction normal to a face of the pick up bar 42 withouthindering the picking action of the pick up bar 42. It also facilitatesmaintaining a trailing portion of the sheet 28.1 in spaced relationshiprelative to the stack 28 while the sheet 28.1 is being fed to the set ofrollers 14.

[0035] The applicant has found that the velocity of air through thefluid hose in the initial, “blowing” direction is not critical, nor isthe spacing between the pick up bar 42 and the topmost sheet 28.1 of thepaper stack 28. Further, the weight or grade of the paper of the stackis also not critical provided that the paper in the stack has a degreeof porosity.

[0036] Typically, a pressure of approximately 5 kPa is present in thefluid hose 14 when the air is blown on to the paper stack 28. The air isdelivered at approximately 11/s and exits the gap between the footportion 58 of the pick up arm 42 and the topmost sheet 28.1 at apressure of approximately 1 kPa at a velocity of approximately 50 m/s.Experimentally, the pick up arm 42 has been held at a spacing of between0.1 mm and 0.2 mm above the paper stack 28 to pick up the topmost sheet28.1 and this has been found to be successful. In addition, the paperfeed arrangement 34 has been found to operate with paper of a grade from40 gsm to high resolution, photo-quality ink jet paper.

[0037] The aperture 54 of the pick up bar 42 can also be any suitableshape. For example, the aperture 54 could be in the form of a straightor wavy channel extending the length of the pick up bar 42. Instead, theaperture could comprise a plurality of discrete nozzles arranged atspaced intervals along the length of the pick up bar 42.

[0038] The applicant has found that, surprisingly, by blowing air on tothe paper of the stack 28 separation of the sheets is facilitated. Thisis an entirely counter-intuitive approach as one would expect that asuction-type mechanism would operate better. However, provided the paperof the stack 28 is porous, very good separation of the topmost sheet ofpaper from the stack 28 can be effected.

[0039] It will be appreciated by persons skilled in the art thatnumerous variations and/or modifications may be made to the invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. A sheet alignment mechanism, comprising: a receptacle to hold sheetmaterial in a stack; a registry stop located at the egress of thereceptacle; and a tapping mechanism located opposite the registry stop,to tap the stack of sheet material in said receptacle to maintain thestack of sheet material in accurate abutment with registry stop.
 2. Thesheet alignment mechanism according to claim 1, wherein the tappingmechanism is solenoid driven.
 3. An alignment mechanism for print mediato be fed to a print feeder mechanism in a printer comprising: areceptacle to hold the print media in a stack; a registry stop locatedat the ingress to the print feed mechanism; and a tapping mechanismlocated opposite the registry stop, to tap the stack of print media insaid receptacle to maintain the stack of print media in accurateabutment with the registry stop, to ensure that when a sheet of printmedia is fed from the stack into the printer it is correctly aligned. 4.An alignment mechanism for print media to be fed to a print feedermechanism in a printer, according to claim 3, wherein the tappingmechanism is solenoid driven.